One form of a method of selectively clamping and releasing a rotary member such as a motor vehicle wheel on a main shaft, which in operation is driven by a motor, of an unbalance measuring arrangement, for example a wheel balancing machine, which involves the use of a pulling rod or bar which is guided movably in the axial direction of the main shaft inside the same, comprises causing a pulling force to be applied to one end of the bar to produce an axial movement of the bar within the main shaft. As a result of that movement, a clamping device at the other end of the bar is brought into clamping and possibly centering engagement with the rotary member to be clamped on the main shaft, such as a vehicle wheel. To release the clamped rotary member, a force which acts in the opposite direction to the direction of the above-mentioned pulling force is caused to act at the end of the bar which is remote from the cladding device to produce an axial release movement in the opposite direction to the axial clamping movement of the bar.
An arrangement which involves that operating procedure, as found in DE 40 00 424 A1, provides for applying a pulling force to the pulling rod or bar by means of a spring to produce the clamping action while, to release the clamped rotary member, the piston of a pneumatic fluid-operated piston-cylinder unit is brought into operation, in opposite relationship to the spring force. Alternatively, a pneumatic fluid-operated piston-cylinder unit can be used in the clamping phase and a spring force can be used in the release phase, in opposite relationship to the action of the piston-cylinder unit.
Another form of clamping arrangement, as found in DE 28 13 387 C2, involves the application of a pulling force to the pulling rod or bar by means of a pneumatic fluid-operated piston-cylinder unit, while release of the clamped wheel involves moving the piston rod in the opposite direction by a spring force or pneumatically.
It will be seen therefore that those items of equipment involve the need for separate energy carriers for the clamping arrangement and for machine drive purposes, being in the form of a spring element and/or compressed air for clamping and releasing a rotary member and electric power for drive purposes. That in turn gives rise to increased expenditure for example on a wheel balancing machine.